I wonder if QRP would be something?

https://hackaday.com/2016/03/08/how-low-can-you-go-the-world...

also

https://en.wikipedia.org/wiki/WSPR_(amateur_radio_software) https://wsjt.sourceforge.io/wsjtx.html

plus the super simple "Fireball QRP transmitter"

https://www.worldradiohistory.com/Archive-DX/73-magazine/73-...